1. Field of the Invention
The present invention relates to an impact power tool for performing a linear hammering operation on a workpiece, and more particularly to a technique for cushioning a reaction force received from the workpiece during hammering operation.
2. Description of the Related Art
Japanese non-examined laid-open Patent Publication No. 8-318342 discloses a technique for cushioning an impact force caused by rebound of a tool bit after its striking movement in a hammer drill. In this known hammer drill, a rubber ring (cushion member) is disposed between the axial end surface of a cylinder on the body side and an intermediate element in the form of an impact bolt which strikes the tool bit When the tool bit receives a reaction force from the workpiece and rebounds after striking movement of the tool bit, the impact bolt collides with the rubber ring. At this time, the rubber ring cushions the impact force by elastic deformation. Further, the rubber ring also functions as a member for positioning the hammer drill body with respect to the workpiece during hammering operation. During the striking movement of the tool bit, the tip end of the tool bit is held pressed against the workpiece (the tool bit is held in its striking position) by application of the user's forward pressing force to the hammer drill body. The cylinder on the body side receives the pressing force via the rubber ring.
As described above, the known rubber ring has a function of cushioning the impact force caused by rebound of the tool bit and a function of positioning the hammer drill. It is advantageous for the rubber ring to be soft in order to absorb the rebound of the tool bit. On the contrary, it is advantageous for the rubber ring to be hard in order to improve the positioning accuracy. In other words, two different properties are demanded of the known rubber ring. It is difficult to provide the rubber ring with a hardness that satisfies the both functional requirements. In this point, further improvement is required.